Hi guys, I've read a lot of posts on rough idle, and it looks like the coil packs, spark plugs, and MAF sensors a big culprits. I'm looking to get a little more input before I go much further with this.

I have an '02 S60 AWD 2.4T with about 126,000 miles on the odo. About 30K miles ago I had the transmission completely replaced at the dealership under warranty. Ever since, I have been getting a random "Reduced Engine Performance" message in the dash. When this happens, there is no perceptible change in performance whatsoever. I've even gone WOT during this condition with no noticeable difference in acceleration from normal. I drive about 240 miles a week and this happens maybe 3-5 times a week.

Fast forward to about a month ago. I started to feel slight misfires during idle (especially noticeable while in drive). This is accompanied by quickly dimming headlights and slight vibration before it goes back to normal. It does this about 5 times at a normal length stop light and each occurrence lasts no longer than a second.

Two weeks ago I decided to go get spark plugs. While on the express way on my way to Auto Zone I went WOT from about 60 MPH to pass and got a flashing Check Engine light, so I backed off and babied it the rest of the way there and back. No more problems.

I replaced the spark plugs with NGK iridiums and made sure the grounds on the coil packs were clean. I also cleaned the coil pack springs with battery terminal cleaner because they looked oxidized, but I don't think they were after all. I also ran a bottle of fuel injector cleaner through one fill-up.

The flashing check engine light does not happen anymore under the same conditions, but I still get the random "Reduced Engine Performance" message, and the regular misfire at idle (sometimes it's worse than others). I'm not sure the two are related, but I figured I'd give all the details.

Is there a process by which I can narrow down the problem? If I have a bad coil, will it miss occasionally, or all the time? What's the best way to clean the MAF? Are there any other things I should check?

I have not yet replaced the timing belt and tensioner, but I have the kit. I'm waiting for a warm spell here in Mighigan. I don't know if that could be part of the problem or not.

Any help would be much appreciated.

Thanks, and sorry for the novel.

 

Have you tried to pull any codes?

 

pull the codes, get check your gaps.

For what its worth, volvo OEM plugs are the best for these cars.

 

I have not pulled any codes, but I will...maybe tonight if I can get to Auto Zone.

As far as plugs are concerned, I read on this forum and others that the NGK iridiums are the OEM plugs minus the Volvo stamp.

 

Not correct - they are Bosch if you have a turbo and Densos if you do not.

 

Bosch what? Which ones am I looking for? Is this a likely culprit for the problem that I'm having?

 

No, probably not.

I BET you have a gap off.

 

OK, well I must admit: I was lazy and it was like -5 degrees out when I changed the plugs, so I didn't check the gaps. That will be my next step (after getting the codes pulled).

Thanks,